Phosphor and phosphor paste

ABSTRACT

A phosphor having a high brightness after being exposed to plasma and a phosphor paste containing the phosphor. The phosphor comprises a fluorescent substance A 1  containing a compound represented by the following formula (I) and at least one activator selected from the group consisting of Eu and Mn, and a fluorescent substance B 1  containing an aluminate;
 
mM 1 O.nM 2 O.2M 3 O 2   (I)
 
[in the formula (I), M 1  is at least two selected from the group consisting of Ca, Sr and Ba, or Ca alone or Ba alone; M 2  is at least one selected from the group consisting of Mg and Zn; M 3  is at least one selected from the group consisting of Si and Ge; 0.5≦m≦3.5; and 0.5≦n≦2.5].

TECHNICAL FIELD

The present invention relates to a phosphor and a phosphor paste.

BACKGROUND ART

Phosphors are used in fluorescent lamps, luminous indications, X-rayinspection systems, CRTs, vacuum ultraviolet excited light-emittingdevices and so on. Known phosphors include aluminates [for example,BaMgAl₁₀O₁₇:Eu] and borates [for example, (Y,Gd)BO₃:Eu] as redphosphors, silicates [for example, CaMgSi₂O₆:Eu] as blue phosphors andsilicates [for example, Zn₂SiO₄:Mn] as green phosphors, and they areused in plasma displays (hereinafter, referred to as PDPs) and vacuumultraviolet excited light-emitting devices such as rare gas lamps.

The vacuum ultraviolet excited light-emitting devices are light-emittingdevices in which plasma is generated by electric discharge in a raregas, and a phosphor is excited by irradiating vacuum ultraviolet raysemitted from the plasma onto the phosphor, thereby resulting in emittingvisible rays from the phosphor.

The brightness of the conventional phosphors decreases when the phosphoris exposed to the plasma.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a phosphor having ahigh brightness even when it is exposed to plasma, and to provide aphosphor paste comprising the phosphor.

As the result of extensive researches for solving the above problemsunder these circumstances, the present inventors have found a phosphorwith a high brightness by combining a specific silicate and aluminateand thus they has completed the present invention.

Therefore, the present invention provides a phosphor comprising afluorescent substance A¹ containing a compound represented by thefollowing formula (I) and at least one activator selected from the groupconsisting of Eu and Mn, and a fluorescent substance B¹ containing analuminate;mM¹O.nM²O.2M³O₂  (I)[in the formula (I),

M¹ is at least two selected from the group consisting of Ca, Sr and Ba,or Ca alone or Ba alone;

M² is at least one selected from the group consisting of Mg and Zn;

M³ is at least one selected from the group consisting of Si and Ge;

0.5≦m≦3.5; and

0.5≦n≦2.5].

Further, the present invention provides a phosphor paste comprising thephosphor, a solvent and a binder.

The phosphor of the present invention has a high brightness after beingexposed to plasma, and is suitable for vacuum ultraviolet excitedlight-emitting devices such as PDP and rare gas lamp. The phosphor andthe phosphor paste provide a vacuum ultraviolet excited light-emittingdevice with a high brightness and a long life.

Mode for carrying out the invention

The phosphor of the present invention includes a fluorescent substanceA¹. The fluorescent substance A¹ contains a compound represented by theabove formula (I) and at least one selected from the group consisting ofEu and Mn as an activator.

In the formula (I),

M¹ is at least two selected from the group consisting of Ca, Sr and Ba,or Ca alone or Ba alone;

M² is at least one selected from the group consisting of Mg and Zn;

M³ is at least one selected from the group consisting of Si and Ge;

0.5≦m≦3.5; and

0.5≦n≦2.5.

It is preferable that the fluorescent substance A¹ is a compoundrepresented by the following formula (II):(M¹ _(1−a)Eu_(a))(M² _(1−b)Mn_(b))M³ ₂O₆  (II)[in the formula (II),

M¹ is at least two selected from the group consisting of Ca, Sr and Ba,or Ca alone or Ba alone;

M² is at least one selected from the group consisting of Mg and Zn;

M³ is at least one selected from the group consisting of Si and Ge;

0≦a≦0.5;

0≦b≦0.5; and

0<a+b].

It is more preferable that the fluorescent substance A¹ is a compoundrepresented by the following formula (III):Ca_(1−c−d)Sr_(c)Eu_(d)MgSi₂O₆  (III)[in the formula (III),

0≦c≦0.1; and

0<d≦0.1].

The phosphor of the present invention includes a fluorescent substanceB¹ other than the fluorescent substance A¹. The fluorescent substance B¹is an aluminate and preferably a compound represented by the followingformula (IV):p(M⁴ _(1−e)Eu_(e))O.q(M⁵ _(1−f)Mn_(f))O.rAl₂O₃  (IV)[in the formula (IV),

M⁴ is at least one selected from the group consisting of Ca, Sr and Ba;

M⁵ is at least one selected from the group consisting of Mg and Zn;

0.5≦p≦1.5;

0.5≦q≦1.5;

4.5≦r≦5.5;

0<e≦0.5; and

0<f≦0.1].

It is preferable that the fluorescent substance B¹ is a compoundrepresented by the following formula (V):Ba_(1−g)Eu_(g)MgAl₁₀O₁₇  (V)[in the formula (V),

0<g≦0.3].

The weight ratio of fluorescent substance A¹/fluorescent substance B¹ ispreferably from 5/95 to 95/5, more preferably from 20/80 to 90/10, andfurther preferably from 30/70 to 85/15. When the weight ratio offluorescent substance A¹/fluorescent substance B¹ is within the aboverange, the obtained phosphor has a higher brightness when it is exposedto plasma.

When the both of the fluorescent substance A¹ and the fluorescentsubstance B¹ are in form of particles, the fluorescent substance A¹ hasa primary particle diameter of usually 0.1 μm to 5 μm, preferably 0.3 μmto 3 μm. The fluorescent substance B¹ has a primary particle diameter ofusually 0.1 μm to 5 μm, preferably 0.3 μm to 3 μm. It is preferable thatD_(B) ¹, the average primary particle diameter of the fluorescentsubstance B¹, is 0.2-5 times D_(A) ¹, the primary particle diameter ofthe fluorescent substance A¹, namely, D_(A) ¹/D_(B) ¹≦5 and D_(B)¹/D_(A) ¹≦5 are satisfied.

The phosphor of the present invention may include other phosphor insofaras it includes the fluorescent substance A¹ and the fluorescentsubstance B¹.

The phosphor of the present invention is excited by vacuum ultravioletrays and has a high brightness, even when it is exposed to plasma. Inthe production of PDP and rare gas lamp, a phosphor layer is formedusually by a production method including steps of mixing a phosphor, abinder and a solvent to obtain a phosphor paste, coating the phosphorpaste on a light-emitting unit, and heat-treating the light-emittingunit (for example, at 500° C.). The phosphor of the present inventionhas a brightness comparable to that before the heat treatment even afterbeing subjected to the heat treatment as described above. Accordingly,when the phosphor of the present invention is used in vacuum ultravioletexcited light-emitting devices such as PDP and a rare gas lamp, PDP anda rare gas lamp with a high brightness and long life can be obtained.

In addition, the phosphor of the present invention is also excited byultraviolet rays, X-rays, electron beams other than vacuum ultravioletrays. The phosphor may be used in fluorescent lamps, luminousindications, X-ray inspection systems, CRTs and so on.

The phosphor with a high brightness according to the present inventionmay be produced, for example, by a method of mixing the fluorescentsubstance A¹ with the fluorescent substance B¹. The mixing may becarried out using an apparatus such as stirrer, ball mill and tripleroller mill. In the mixing, a phosphor other than the fluorescentsubstance A¹ and the fluorescent substance B¹ may be added, ifnecessary.

The fluorescent substance A¹ may be prepared, for example, by calcininga mixture of metal compounds which is converted to the fluorescentsubstance A¹ by calcination.

Examples of calcium source, strontium source, barium source(corresponding to M¹ in the formula (I)) in the mixture include acompound which is decomposed to be an oxide at high temperature such ashydroxide, carbonate, nitrate, halide and oxalate having a purity of notless than 99%, or an oxide having a purity of not less than 99.9%.

Examples of magnesium source, zinc source (corresponding to M² in theformula (I)) in the mixture include a compound which is decomposed to bean oxide at high temperature such as hydroxide, carbonate, nitrate,halide and oxalate having a purity of not less than 99%, or an oxidehaving a purity of not less than 99%.

Examples of silicon source, germanium source (corresponding to M³ in theformula (I)) in the mixture include a compound which is decomposed to bean oxide at high temperature such as hydroxide, carbonate, nitrate,halide and oxalate having a purity of not less than 99%, or an oxidehaving a purity of not less than 99%.

Examples of europium source, manganese source (an activator for thefluorescent substance A¹) in the mixture include a compound which isdecomposed to be an oxide at high temperature such as hydroxide,carbonate, nitrate, halide and oxalate having a purity of not less than99%, or an oxide having a purity of not less than 99%.

The fluorescent substance A¹ is prepared by mixing the above compoundsweighed such that predetermined composition of fluorescent substance A¹is obtained and calcining the mixture.

The mixing may be carried out, for example, using a ball mill, V-typemixer or stirrer. In the mixing, an appropriate amount of a flux may beadded. By addition of a flux, the formation of the phosphor is promotedand calcination at a lower temperature becomes possible.

The calcination is preferably carried out under a reductive atmosphere,for example, under nitrogen atmosphere containing about 0.1% by volumeto about 10% by volume of hydrogen, or argon atmosphere containing about0.1% by volume to about 10% by volume of hydrogen. Usually, thecalcination may be carried out under conditions of temperature of fromabout 1,000° C. to about 1,500° C. and time of from about 1 hour toabout 100 hours.

When the mixture contains a compound which is decomposed to be an oxideat high temperature such as hydroxide, carbonate, nitrate, halide andoxalate, the mixture may be pre-calcined before the calcination.

The pre-calcination may be carried out under any of oxidative atmosphere(for example, under air) and reductive atmosphere. The pre-calcinationmay usually be conducted at temperature of from about 600° C. to about900° C.

The fluorescent substance A¹ may be pulverized, washed or classified, ifnecessary. The pulverization may be carried out, for example, using aball mill or jet mill. The pulverized fluorescent substance A¹ may beheat-treated. Crystallinity of the fluorescent substance A¹ (which islowered by pulverization) may be enhanced by the heat treatment. Theheat treatment may usually be carried out under the same conditions asthose for the calcination described above.

Further, the fluorescent substance A¹ used in the present invention maybe prepared, for example, by a method described in JP-A-2002-332481 orJP-A-2003-183644.

The fluorescent substance B¹ may be prepared, for example, by calcininga mixture of metal compounds which is converted to the fluorescentsubstance B¹ by calcination.

When the fluorescent substance B¹ contains, for example, barium (Ba),europium (Eu), magnesium (Mg), aluminum (Al) and oxygen (O):

Examples of barium source, europium source, magnesium source, andaluminum source in the mixture include a compound which is decomposed tobe an oxide at high temperature and an oxide having a purity of not lessthan 99.9%.

The fluorescent substance B¹ is prepared by mixing the above compoundsweighed such that predetermined composition of fluorescent substance B¹is obtained and calcining the mixture.

The mixing, calcination and optional pre-calcination may be carried outunder the same conditions as those for the fluorescent substance A¹. Thefluorescent substance B¹ obtained by calcination may be pulverized,washed or classified, if necessary. The pulverization may be carriedout, for example, using a ball mill or jet mill. The pulverizedfluorescent substance B¹, may be heat-treated. Crystallinity of thefluorescent substance B¹ (which is lowered by pulverization) can beenhanced by the heat treatment. The heat treatment may usually becarried out under the same conditions as those for the calcinationdescribed above.

Further, the fluorescent substance B¹ used in the present invention maybe prepared, for example, by a method described in JP-A-2001-220582.

The phosphor paste according to the present invention is described.

The phosphor paste of the present invention includes the above phosphor,a binder and a solvent. A film or a layer can easily be formed on asubstrate by coating the phosphor paste on the substrate and heating.The heating is usually carried out at a temperature not lower than atemperature at which the solvent evaporates and lower than a temperatureat which the binder decomposes.

The phosphor paste of the present invention may be produced, forexample, by a method of mixing the fluorescent substance A¹, thefluorescent substance B¹, a solvent and a binder using an apparatus suchas a ball mill, triple roller mill, beads mill and roller mill.

Examples of the binder in the phosphor paste include cellulose resins(ethylcellulose, methylcellulose, nitrocellulose, acetylcellulose,cellulose propionate, hydroxypropylcellulose, butylcellulose,benzylcellulose, modified cellulose and the like), acryl resins(polymers of at least one among monomers including acrylic acid,methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate,ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropylacrylate, isopropyl methacrylate, n-butyl acrylate, n-butylmethacrylate, tert-butyl acrylate, tert-butyl methacrylate,2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropylacrylate, 2-hydroxypropyl methacrylate, benzyl acrylate,benzylmethacrylate, phenoxyacrylate, phenoxymethacrylate, isobornylacrylate, isobornyl methacrylate, glycidyl methacrylate, styrene,α-methylstyrene, acrylamide, methacrylamide, acrylonitrile,methacrylonitrile and the like), ethylene-vinyl acetate copolymerresins, polyvinyl butyral, polyvinyl alcohol, propylene glycol, urethaneresins, melamine resins and phenol resins.

The amount of the binder is usually 5% by weight to 50% by weight basedon the total weight of the fluorescent substance A¹ and the fluorescentsubstance B¹.

Examples of the solvent in the phosphor paste include monohydricalcohols having a higher boiling point; polyhydric alcohols such asdiols and triols typically exemplified by ethylene glycol and glycerin;compounds formable by etherifying or esterifying an alcohol (ethyleneglycol monoalkyl ether, ethylene glycol dialkyl ether, ethylene glycolalkyl ether acetate, diethylene glycol monoalkyl ether acetate,diethylene glycol dialkyl ether, propylene glycol monoalkyl ether,propylene glycol dialkyl ether and propylene glycol alkyl acetate).

The amount of the solvent is usually 100% by weight to 600% by weightbased on the total weight of the fluorescent substance A¹ and thefluorescent substance B¹.

EXAMPLES

The present invention will be explained in more detail by followingexamples, which should not be constructed as limiting the invention inany manner.

The brightness of the specimen (phosphor) is measured by the followingmethod:

A specimen is heat-treated in the air at 500° C. for 30 minutes and, isexposed to a plasma of 50 W for 15 minutes under an atmosphere of a gascomposition: 5% by volume of xenon (Xe) and 95% by volume of neon (Ne)and a pressure: 13.2 Pa.

The obtained specimen was irradiated by vacuum ultraviolet rays usingExcimer 146 nm lamp (model H0012, made by Ushio Denki) in a vacuumchamber under pressure of 6.7 Pa (5×10⁻² Torr) or lower.

Reference 1

The brightness of an aluminate (Ba_(0.9)Eu_(0.1)MgAl₁₀O₁₇, a bluefluorescent substance, average primary particle diameter: 0.4 μm) wasmeasured according to the above method. The brightness of the aluminatewas assumed be 100.

Reference 2

The brightness of a silicate (Ca_(0.9215)Sr_(0.0485)Eu_(0.03)MgSi₂O₆, ablue fluorescent substance, average primary particle diameter: 1.0 μm)was measured according to the above method. The silicate had abrightness of 104.

Example 1

50 parts by weight of the fluorescent substance in Reference 2 werewet-mixed with 50 parts by weight of the fluorescent substance inReference 1 in ethanol to obtain a mixture. The mixture was dried toobtain a phosphor. The brightness of the phosphor was measured. Thephosphor emitted blue light and had a brightness of 127.

Example 2

80 parts by weight of the fluorescent substance in Reference 2 werewet-mixed with 20 parts by weight of the fluorescent substance inReference 1 in ethanol to obtain a mixture. The mixture was dried toobtain a phosphor. The brightness of the phosphor was measured. Thephosphor emitted blue light and had a brightness of 113.

Example 3

20 parts by weight of the fluorescent substance in Reference 2 werewet-mixed with 80 parts by weight of the fluorescent substance inReference 1 in ethanol to obtain a mixture. The mixture was dried toobtain a phosphor. The brightness of the phosphor was measured. Thephosphor emitted blue light and had a brightness of 107.

1. A phosphor comprising a fluorescent substance A¹ containing a compound represented by the following formula (II) and at least one activator selected from the group consisting of Eu and Mn, and a fluorescent substance B¹ containing an aluminate: (M¹ _(1−a)Eu_(a))(M² _(1−b)Mn_(b))M³ ₂O₆  (II) wherein M¹ is at least two selected from the group consisting of Ca, Sr and Ba, or Ca alone or Ba alone; M² is at least one selected from the group consisting of Mg and Zn; M³ is at least one selected from the group consisting of Si and Ge; 0≦a≦0.5; 0≦b≦0.5; and 0<a+b; and wherein the weight ratio of fluorescent substance A¹/fluorescent substance B¹ is from 5/95 to 95/5.
 2. The phosphor according to claim 1, wherein the fluorescent substance A¹ is a compound represented by the following formula (III): Ca_(1−c−d)Sr_(c)Eu_(d)MgSi₂O₆  (III) wherein 0≦c≦0.1; and 0<d≦0.1.
 3. The phosphor according to claim 1, wherein the aluminate is a compound represented by the following formula (IV): p(M⁴ _(1−e)Eu_(e))O.q(M⁵ _(1−f)Mn_(f))O.rAl₂O₃  (IV) wherein M⁴ is at least one selected from the group consisting of Ca, Sr and Ba; M⁵ is at least one selected from the group consisting of Mg and Zn; 0.5≦p≦1.5; 0.5≦q≦1.5; 4.5≦r≦5.5; 0<e≦0.5; and 0<f≦0.1.
 4. The phosphor according to claim 1, wherein the aluminate is a compound represented by the following formula (V): Ba_(1−g)Eu_(g)MgAl₁₀O₁₇  (V) wherein, 0<g≦0.3.
 5. The phosphor according to claim 1, wherein the fluorescent substance B¹ is in form of particles and D_(B) ¹ that is the average primary particle diameter of the fluorescent substance B¹ is 0.2-5 times D_(A) ¹ that is the primary particle diameter of the fluorescent substance A¹.
 6. A phosphor paste comprising the phosphor according to claim 1, a solvent and a binder.
 7. A vacuum ultraviolet excited light-emitting device comprising the phosphor according to claim
 1. 